1. Field
This invention relates to battery chargers. More particularly, this invention provides for a solid state battery charger which receives power from a variable voltage direct current power source and supplies a multi-mode charging program having a constant current in selected mode related to the state of charge of the battery under charge and which is particularly suitable for use with vehicles and especially aircraft.
2. State of the Art
In many applications batteries are used as a temporary or emergency source of power. For example, in certain kinds of vehicles (e.g., aircraft), batteries act as a source of power for starting engines and as an emergency source of power in the event the generator typically associated with the engines of the vehicle fails. For such applications, it is important to return the battery to and maintain it in a fully charge condition after use. However, it is well known that charging a battery to and maintaining it in a fully charged condition is a multifaceted problem involving many factors. For example, battery type, battery age and useful life, available charging power, physical environment, and battery capacity are just some of the factors to be considered in selecting not only the battery to be used but also the battery charger and charging program to optimally charge and recharge the battery.
In some applications, it is essential that the battery be rapidly, safely and fully charged from whatever level of discharge of the battery, including deep discharge. Further, it may also be important that charging be done automatically and reliably. This is particularly important for vehicles in which the battery is required to reliably deliver starting power and/or act as a reliable source of emergency power because of the nature of the vehicle's environment or use. Such vehicles include aircraft, military tanks, power boats, surface effect watercraft, certain recreational (e.g., off-the-road) vehicles and the like. In other applications, the type of battery used suggests that the battery be properly and efficiently charged to prolong battery life and to improve battery effectiveness and performance. For example, heavy equipment (i.e., bulldozers, graders, etc.) vehicles and other diesel engine equipment may use expensive high capacity batteries which should be optimally charged to prolong their life and effectiveness.
Battery charging for aircraft and especially high altitude aircraft is further complicated by additional platform and environmental factors. For example, as altitude increases, less air is available for cooling and gasing during charge can be more significant. The cold temperatures during winter months or at high altitudes (e.g., above about 30,000 feet) can have an adverse effect on the battery charger and the battery. In aircraft it is frequently desirable to minimize weight. In turn, the power source typically associated with the engine (e.g., generator/alternator) may not have extensive voltage regulation to eliminate weight. However, typical battery chargers are not readily adaptable to or efficient when used with variable voltage power supplies.
U.S. Pat. No. 4,061,956, issued Dec. 6, 1977, discloses an electronic battery charger suitable for use with aircraft. However, the charger therein disclosed is not optimally efficient (about 80%) and generates enough heat to be less than optimum for use especially with aircraft. Further, the charger disclosed in U.S. Pat. No. 4,061,956 is suited for use with voltages that do not exceed about 29 volts and is not adaptable for use with a power supply that varies widely in voltage (e.g., from about 26 volts to about 35 volts DC).
A high efficient charger that is lightweight, reliable and suitable for use with a widely varying source voltage is not available.